/***
 * ASM: a very small and fast Java bytecode manipulation framework Copyright (c) 2000-2011 INRIA,
 * France Telecom All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted
 * provided that the following conditions are met: 1. Redistributions of source code must retain the
 * above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions
 * in binary form must reproduce the above copyright notice, this list of conditions and the
 * following disclaimer in the documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the copyright holders nor the names of its contributors may be used to
 * endorse or promote products derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
 * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package com.googlecode.aviator.asm;

/**
 * A non standard class, field, method or code attribute.
 *
 * @author Eric Bruneton
 * @author Eugene Kuleshov
 */
public class Attribute {

    /**
     * The type of this attribute.
     */
    public final String type;

    /**
     * The raw value of this attribute, used only for unknown attributes.
     */
    byte[] value;

    /**
     * The next attribute in this attribute list. May be <tt>null</tt>.
     */
    Attribute next;

    /**
     * Constructs a new empty attribute.
     *
     * @param type the type of the attribute.
     */
    protected Attribute(final String type) {
        this.type = type;
    }

    /**
     * Returns <tt>true</tt> if this type of attribute is unknown. The default implementation of this
     * method always returns <tt>true</tt>.
     *
     * @return <tt>true</tt> if this type of attribute is unknown.
     */
    public boolean isUnknown() {
        return true;
    }

    /**
     * Returns <tt>true</tt> if this type of attribute is a code attribute.
     *
     * @return <tt>true</tt> if this type of attribute is a code attribute.
     */
    public boolean isCodeAttribute() {
        return false;
    }

    /**
     * Returns the labels corresponding to this attribute.
     *
     * @return the labels corresponding to this attribute, or <tt>null</tt> if this attribute is not a
     * code attribute that contains labels.
     */
    protected Label[] getLabels() {
        return null;
    }

    /**
     * Reads a {@link #type type} attribute. This method must return a <i>new</i> {@link Attribute}
     * object, of type {@link #type type}, corresponding to the <tt>len</tt> bytes starting at the
     * given offset, in the given class reader.
     *
     * @param cr      the class that contains the attribute to be read.
     * @param off     index of the first byte of the attribute's content in {@link ClassReader#b cr.b}.
     *                The 6 attribute header bytes, containing the type and the length of the attribute, are
     *                not taken into account here.
     * @param len     the length of the attribute's content.
     * @param buf     buffer to be used to call {@link ClassReader#readUTF8 readUTF8},
     *                {@link ClassReader#readClass(int, char[]) readClass} or {@link ClassReader#readConst
     *                readConst}.
     * @param codeOff index of the first byte of code's attribute content in {@link ClassReader#b
     *                cr.b}, or -1 if the attribute to be read is not a code attribute. The 6 attribute header
     *                bytes, containing the type and the length of the attribute, are not taken into account
     *                here.
     * @param labels  the labels of the method's code, or <tt>null</tt> if the attribute to be read is
     *                not a code attribute.
     * @return a <i>new</i> {@link Attribute} object corresponding to the given bytes.
     */
    protected Attribute read(final ClassReader cr, final int off, final int len, final char[] buf,
                             final int codeOff, final Label[] labels) {
        Attribute attr = new Attribute(type);
        attr.value = new byte[len];
        System.arraycopy(cr.b, off, attr.value, 0, len);
        return attr;
    }

    /**
     * Returns the byte array form of this attribute.
     *
     * @param cw        the class to which this attribute must be added. This parameter can be used to add to
     *                  the constant pool of this class the items that corresponds to this attribute.
     * @param code      the bytecode of the method corresponding to this code attribute, or <tt>null</tt>
     *                  if this attribute is not a code attributes.
     * @param len       the length of the bytecode of the method corresponding to this code attribute, or
     *                  <tt>null</tt> if this attribute is not a code attribute.
     * @param maxStack  the maximum stack size of the method corresponding to this code attribute, or
     *                  -1 if this attribute is not a code attribute.
     * @param maxLocals the maximum number of local variables of the method corresponding to this code
     *                  attribute, or -1 if this attribute is not a code attribute.
     * @return the byte array form of this attribute.
     */
    protected ByteVector write(final ClassWriter cw, final byte[] code, final int len,
                               final int maxStack, final int maxLocals) {
        ByteVector v = new ByteVector();
        v.data = value;
        v.length = value.length;
        return v;
    }

    /**
     * Returns the length of the attribute list that begins with this attribute.
     *
     * @return the length of the attribute list that begins with this attribute.
     */
    final int getCount() {
        int count = 0;
        Attribute attr = this;
        while (attr != null) {
            count += 1;
            attr = attr.next;
        }
        return count;
    }

    /**
     * Returns the size of all the attributes in this attribute list.
     *
     * @param cw        the class writer to be used to convert the attributes into byte arrays, with the
     *                  {@link #write write} method.
     * @param code      the bytecode of the method corresponding to these code attributes, or <tt>null</tt>
     *                  if these attributes are not code attributes.
     * @param len       the length of the bytecode of the method corresponding to these code attributes, or
     *                  <tt>null</tt> if these attributes are not code attributes.
     * @param maxStack  the maximum stack size of the method corresponding to these code attributes, or
     *                  -1 if these attributes are not code attributes.
     * @param maxLocals the maximum number of local variables of the method corresponding to these
     *                  code attributes, or -1 if these attributes are not code attributes.
     * @return the size of all the attributes in this attribute list. This size includes the size of
     * the attribute headers.
     */
    final int getSize(final ClassWriter cw, final byte[] code, final int len, final int maxStack,
                      final int maxLocals) {
        Attribute attr = this;
        int size = 0;
        while (attr != null) {
            cw.newUTF8(attr.type);
            size += attr.write(cw, code, len, maxStack, maxLocals).length + 6;
            attr = attr.next;
        }
        return size;
    }

    /**
     * Writes all the attributes of this attribute list in the given byte vector.
     *
     * @param cw        the class writer to be used to convert the attributes into byte arrays, with the
     *                  {@link #write write} method.
     * @param code      the bytecode of the method corresponding to these code attributes, or <tt>null</tt>
     *                  if these attributes are not code attributes.
     * @param len       the length of the bytecode of the method corresponding to these code attributes, or
     *                  <tt>null</tt> if these attributes are not code attributes.
     * @param maxStack  the maximum stack size of the method corresponding to these code attributes, or
     *                  -1 if these attributes are not code attributes.
     * @param maxLocals the maximum number of local variables of the method corresponding to these
     *                  code attributes, or -1 if these attributes are not code attributes.
     * @param out       where the attributes must be written.
     */
    final void put(final ClassWriter cw, final byte[] code, final int len, final int maxStack,
                   final int maxLocals, final ByteVector out) {
        Attribute attr = this;
        while (attr != null) {
            ByteVector b = attr.write(cw, code, len, maxStack, maxLocals);
            out.putShort(cw.newUTF8(attr.type)).putInt(b.length);
            out.putByteArray(b.data, 0, b.length);
            attr = attr.next;
        }
    }
}
